Question 1186801
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Let x = sales, in dollars.


Then your equation is


    1-st company   =  2-nd company

       0.04x       =   420 + 0.02x


Simplify and find x :


       0.04x - 0.02x = 420

           0.02x     = 420

               x     = {{{420/0.02}}} = {{{42000/2}}} = 21000  dollars.


<U>ANSWER</U>.  The sales under the problem's question should be  $21000.
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Solved.